Tube and fin type heat exchangers are widely used in a number of industries in a wide variety of different applications. Such heat exchangers generally consist of a number of parallel tubes having a plurality of closely spaced heat conductive fin members positioned transversely across them with tubes passing through holes in the fins and contacting the fins in heat conducting relationship. A first fluid is caused to be circulated through the tubes, either in a single parallel flow pass, or, through the use of suitable return bends, through one or more return passes. A second fluid is directed to flow along and between the fins and around the tubes in heat conducting relationship to the tubes and fins. Single or multiple passes of the second fluid medium can be provided through the use of baffles as is well known. The physical dimensions and choice of materials depend, of course, on the specific application for the heat exchanger, including type of fluid, i.e. oil, water, refrigerant, air, etc., temperature and pressure range and difference requirements and the like. The fins are secured to the tubes, for example, by metallurgical bonding or by expansion of the tubes after insertion through the apertures provided in the fins, so as to create good thermal contact and heat transfer so that the fins act to increase the surface area of the tubes to increase heat transfer.
Heat transfer efficiency is diminished in such heat exchangers because the second fluid medium flowing along the fins tends to build up boundary or viscous layers adjacent the fins. The viscous layer starts at the leading edge of a fin and tends to grow in thickness as the fluid moves across the fin. The viscous layer tends to act as a heat insulation barrier, degrading performance. The longer the flow path, the thicker the boundary layer and the poorer the performance. Various types of patterns have been applied to the fins in the prior art to increase heat transfer such as projections, indentations and undulations, and various types of openings such as slits, louvers, and holes. Regardless of the particular shape, a primary purpose of the patterns is to break up the boundary or viscous layer and promote some turbulence to aid in heat transfer without building up excessive amounts of pressure drop. Some such techniques have succeeded better than others, and the test for whether a particular pattern is better than others depends in many cases on the parameters of the specific application in terms of types of fluid, temperature and pressure differences, and the flow rates of the two fluids. Thus there is not a universally recognized best tube and heat exchanger construction or patterned fins therefor.
Despite progress that has been made in the field, there is always incentive for further improvement, because an increase in heat transfer efficiency translates into a savings in cost of material for a given heat exchanger or reduces operating pressure drop which results in a savings of power for associated equipment, both of which in turn result in greater economies. Improvements of even small percentages in overall efficiencies can lead to significant manufacturing and operational savings.
This invention provides a new fin pattern for a fin and tube heat exchanger providing improved heat exchange efficiency with minimal increase in pressure drop for certain types of applications. The heat exchanger of this invention has been found to provide significant improvements as applied to an engine aftercooler or intercooler in which hot air directed across and through the fins is cooled by liquid circulated through the tubes. In addition, the invention is useful in related types of heat exchangers.